HI Lynne
On Wed, Jan 13, 2021 at 10:30 AM Lynne <d...@lynne.ee> wrote:
> Jan 13, 2021, 18:46 by tfo...@gmail.com:
>
> > By default the time code scale in a MKV file in millisecond. With this
> > option we can set the time code scale to microsecond or nanoseconds for
> > very high frame rate.
> > ---
> > libavformat/matroskaenc.c | 11 +++++++----
> > 1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
> > index 233c472b8f..cfad6a4693 100644
> > --- a/libavformat/matroskaenc.c
> > +++ b/libavformat/matroskaenc.c
> > @@ -158,6 +158,8 @@ typedef struct MatroskaMuxContext {
> > int default_mode;
> >
> > uint32_t segment_uid[4];
> > +
> > + int64_t timecodescale;
> > } MatroskaMuxContext;
> >
> > /** 2 bytes * 7 for EBML IDs, 7 1-byte EBML lengths, 6 1-byte uint,
> > @@ -1827,7 +1829,7 @@ static int mkv_write_header(AVFormatContext *s)
> > return ret;
> > pb = mkv->info.bc;
> >
> > - put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000);
> > + put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, mkv->timecodescale);
> > if ((tag = av_dict_get(s->metadata, "title", NULL, 0)))
> > put_ebml_string(pb, MATROSKA_ID_TITLE, tag->value);
> > if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
> > @@ -1927,12 +1929,12 @@ static int mkv_write_header(AVFormatContext *s)
> > // after 4k and on a keyframe
> > if (IS_SEEKABLE(pb, mkv)) {
> > if (mkv->cluster_time_limit < 0)
> > - mkv->cluster_time_limit = 5000;
> > + mkv->cluster_time_limit = 5*(1000000000/mkv->timecodescale);
> > if (mkv->cluster_size_limit < 0)
> > mkv->cluster_size_limit = 5 * 1024 * 1024;
> > } else {
> > if (mkv->cluster_time_limit < 0)
> > - mkv->cluster_time_limit = 1000;
> > + mkv->cluster_time_limit = 1*(1000000000/mkv->timecodescale);
> > if (mkv->cluster_size_limit < 0)
> > mkv->cluster_size_limit = 32 * 1024;
> > }
> > @@ -2708,7 +2710,7 @@ static int mkv_init(struct AVFormatContext *s)
> > }
> >
> > // ms precision is the de-facto standard timescale for mkv files
> > - avpriv_set_pts_info(st, 64, 1, 1000);
> > + avpriv_set_pts_info(st, 64, 1, 1000000000/mkv->timecodescale);
> >
> > if (st->codecpar->codec_type == AVMEDIA_TYPE_ATTACHMENT) {
> > if (mkv->mode == MODE_WEBM) {
> > @@ -2795,6 +2797,7 @@ static const AVOption options[] = {
> > { "infer", "For each track type, mark the first track of disposition
> default as default; if none exists, mark the first track as default.", 0,
> AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER }, 0, 0, FLAGS,
> "default_mode" },
> > { "infer_no_subs", "For each track type, mark the first track of
> disposition default as default; for audio and video: if none exists, mark
> the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 =
> DEFAULT_MODE_INFER_NO_SUBS }, 0, 0, FLAGS, "default_mode" },
> > { "passthrough", "Use the disposition flag as-is", 0,
> AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_PASSTHROUGH }, 0, 0, FLAGS,
> "default_mode" },
> > + { "timecodescale", "Time code scale for all tracks in nanoseconds",
> OFFSET(timecodescale), AV_OPT_TYPE_INT64, { .i64 = 1000000 }, 1,
> 1000000000, FLAGS },
> > { NULL },
> > };
> >
>
> This, x10000000000000000!
> Can we make it 1ns by default? Or maybe autodetect the highest precision
> timebase of all streams and use it?
>
The MKV spec seems to indicate a default value of ms. I did not want to
change it in this patch.
> Let's not keep generating garbage files with shitty rounding that players
> have to work around to recover the original timestamp based on framerate
> to reduce jitter (mpv does this!).
>
+1 on this, but I'm worry, we could break a lot of decoder which may not
follow the correct timecodescale (Which we found out in our system a while
back)
> Also WebM mode should disable this, because the spec is dumb and specifies
> a 1ms precision for no good reason.
>
If we keep the default value of ms, then this will not change any webm
unless a user decides to generate a Webm file and set this flag.
Do you want me to log an error saying that using this flag to set something
other than ms for webm is incorrect?
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--
Thierry Foucu
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